The causes and dynamics of the Permian-Triassic boundary (PTB) mass extinction, the largest in Earth history, remain uncertain. Gradual deterioration of marine and terrestrial environments during the Late Permian and persistence of inhospitable conditions through the Early Triassic suggest that intrinsic factors were important, but an extinction rate peak, abrupt lithofacies changes, and geochemical anomalies associated with the end-Permian event horizon are evidence of a catastrophic event (e.g., massive volcanic eruption, bolide impact, and/or large-scale oceanic overturn). Despite long study of the PTB, there are remarkably few integrated, high-resolution chemostratigraphic studies of marine boundary sections that can address critical questions related to the extent and intensity of Permo-Triassic deep-ocean anoxia, patterns of upwelling of toxic deep-ocean waters onto shallow-marine shelves and platforms, the relationship of such events to contemporaneous changes in seawater carbonate saturation and to the delayed recovery of marine biotas, controls on the post-extinction global negative C-isotope shift, and the relative timing and causal relationship of PTB crises in the marine and terrestrial realms. In this project, we propose to generate geochemical proxy datasets consisting of magnetic susceptibility, elemental concentrations, TOC-TIC, ?Ô13Ccarb-?Ô13Corg, S-Fe speciation, ?Ô34Ssulfide-?Ô34Ssulfate, REEs, and biomarkers for a total of 19 sections in eight study areas, including 8 sections in four areas of the former Panthalassic Ocean (the Cache Creek terrane, Western Sedimentary Basin, and Sverdrup Basin of Canada, and the Maitai-Waipapa terranes of New Zealand) and 11 sections in four areas of the former Tethys Ocean (Vietnam-China, India, Iran, and Italy). Conodont biostratigraphy combined with C-isotope and MS event stratigraphy will facilitate correlations within and between study areas. Paleoceanographic modeling will be used to investigate the effects of potential forcings on Permo-Triassic ocean chemistry and sedimentary fluxes, and comparisons with globally integrated chemostratigraphic datasets will allow refinement of model simulations. This project has the potential to yield important new findings regarding events at the Permian-Triassic boundary and key insights regarding proximate and ultimate controls on contemporaneous chemical oceanographic perturbations. Investigation of catastrophic climate and environmental change associated with the largest mass extinction in Earth history should be of considerable interest to both the Earth-science community and the scientifically literate public. The broader impacts of the project are varied and include public outreach and dissemination of project results, mentoring of undergraduate and graduate students, development of research synergies among a diverse group of geoscience professionals, and the potential for results of broad scientific significance. The PIs are committed to training the next generation of scientists (they have collectively supervised ~60 graduate students, and all are actively engaged in advising and training undergraduate students), to advancing science education in the public schools, and to achieving greater ethnic and gender diversity among these future scholars (Algeo and Ellwood are both involved in programs to recruit minority students). Project datasets funded through NSF will be made available to the larger scientific community through CHRONOS and PaleoStrat.
Intellectual Merit Catastrophic events such as mass extinctions in the Earth’s past have intrigued scientists as well as the general public since a long time. The Permian-Triassic boundary (~252 million years ago) is characterized by the extinction of ~90% of all marine species and widespread devastation of terrestrial ecosystems, representing the largest mass extinction in Earth history. The causes and dynamics of the Permian-Triassic mass extinction remain uncertain. Both gradual changes of marine and terrestrial environments during the Late Permian, as well as massive volcanic eruptions in Siberia, triggering a series of events, were probably important. Protracted oceanic anoxic events for this time, especially in shallow marine areas, have been inferred from sedimentary data. In this study, effects of changes in nutrient and dust fluxes, and of the efficiency of the carbon transfer into the deep-sea at the Permian-Triassic boundary have been investigated. The analysis of these climate simulations indicates that around the Permian-Triassic boundary, the oxygen minimum zone expanded considerably, while the deep Panthalassa, the super ocean during the Permian, remained ventilated (see figure). The warming-induced increase in low-oxygen conditions within the water column aggravated adverse existing conditions and likely contributed to the extinction peak. Widespread deep-sea anoxia, generated by a strong increase in weathering and the related enhanced nutrient input into the oceans, was probably closely linked to the delayed recovery of species in the Early Triassic. Periodic upwelling of low-oxygen water masses can be amplified by Earth’s orbital parameters, in particular extremes in precession of the equinoxes Analysis of climate simulations with extreme orbital parameters suggests a high variability in precipitation during megamonsoons, trade winds and equatorial upwelling. These climatic fluctuations led to changes in the export of carbon from the euphotic zone and in dissolved oxygen concentrations in subsurface layers. The model results suggest that orbital variability, as identified in the sedimentary record, and the associated extinction of species are related to periodic ocean anoxia in near surface-to-intermediate depth. Moreover, the response of Late Permian climates to varying increases in the greenhouse gas concentration has been investigated. Equatorial sea surface temperatures were predicted to be ~30°C, about 3°C warmer than at present-day, for a climate simulation with four times the preindustrial atmospheric carbon dioxide concentration. The data-inferred rapid temperature change across the Permian-Triassic boundary in the equatorial Pacific to up to 40°C for the Early Triassic may require a carbon pulse of almost 9000 PgC, which would be about twice the amount of the current fossil fuel inventories. However, a comparison of simulated biomes, which are climatically and geographically defined as contiguous areas with similar climatic conditions, for the Late Permian shows a better match with the reconstructions for greenhouse gas concentrations comparable to the emissions that would arise from the burning of all present fossil fuel inventories. To solve this discrepancy between data and model, a climate change simulation with altered cloud optical thickness has been performed. Cloud properties might have changed across the Permian-Triassic due to reduced marine biological production in response to overall warming. The analysis of this climate simulation reveals a warming over the ocean of ~4°C, with high tropical temperatures of ~36°C, in good agreement with data-derived temperature estimates. High-latitude warming and increased high-latitude rainfall in this climate simulation with reduced cloud optical thickness led to enhanced stratification of water masses due to an increase in the vertical thermal gradient and to diminished oxygen concentration in the deep sea. The environmental stress associated with the ocean warming, shift in water masses, and decrease in the oxygen concentration could have contributed to the extinction of marine organisms. Broader Impact Future climate simulations indicate a warmer ocean with a reduced overturning circulation. Such circumstances may be comparable to the conditions at the Permian-Triassic boundary where large areas of the deep Panthalassa, the global ocean surrounding the supercontinent Pangea, may have been anoxic. This project has yielded important new findings regarding controls on Permian-Triassic chemical oceanographic perturbations, but also regarding processes within the ocean-carbon cycle-sediment system in general. Project results have been disseminated through numerous scientific publications, presentations at national and international scientific meetings, as well as outreach events. A project website has been generated which contains a description of the main results as links to publications (www.uta.edu/faculty/awinguth/ptb_research/ptb_ccsm.html). A female graduate student has completed her Ph.D. Thesis within this project. In addition, collaboration with the NSF-funded AUGMENTS program has occurred, enabling students from underrepresented groups and with financial needs to pursue a career in the geosciences (http://grad.pci.uta.edu/programs/augments/).
